Oxide superconducting wire material, superconducting conductor, and superconducting coil

Abstract

This oxide superconducting wire material comprises: a tape-like metal substrate made of a nickel alloy; an intermediate layer laid on the metal substrate; and an oxide superconducting layer laid on the intermediate layer. The Vickers hardness of the metal substrate is 230 HV or more.

Description

Oxide superconducting wire, superconducting conductor, and superconducting coil

[0001] The present invention relates to an oxide superconducting wire, a superconducting conductor, and a superconducting coil. This application claims priority to Japanese Patent Application No. 2024-055491, filed on March 29, 2024, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses a superconducting wire having a metal substrate, an intermediate layer, and a superconducting layer. A plurality of such superconducting wires are joined by a connecting wire and used as a single superconducting conductor.

[0003] Japanese Patent Application Publication No. 2013-235699

[0004] When a superconducting conductor such as that described in Patent Document 1 is wound and used as a coil, there is a portion where the connecting wire and the superconducting wire overlap in the radial direction. At this overlapping portion, a step corresponding to the thickness of the connecting wire applies a radial pressure to the superconducting wire (thickness direction of the wire) due to stress applied in the radial direction of the coil during operation and tension applied to wind the coil. This pressure may cause deformation of the metal substrate and deterioration of the superconducting layer, resulting in a decrease in superconducting properties.

[0005] The present invention has been made in consideration of the above circumstances, and has as its object to provide an oxide superconducting wire, a superconducting conductor, and a superconducting coil in which the deterioration of superconducting properties due to pressing force in the thickness direction is suppressed.

[0006] An oxide superconducting wire according to a first aspect of the present invention comprises a tape-shaped metal substrate made of a nickel alloy, an intermediate layer laminated on the metal substrate, and an oxide superconducting layer laminated on the intermediate layer, wherein the metal substrate has a Vickers hardness of 230 HV or more.

[0007] In the oxide superconducting wire according to the first aspect, the metal substrate has a Vickers hardness of 230 HV or more, which makes it possible to suppress deformation of the metal substrate when an object is pressed against the metal substrate, thereby suppressing deterioration of the superconducting properties due to deterioration of the superconducting layer accompanying deformation of the metal substrate.

[0008] A second aspect of the present invention is the oxide superconducting wire according to the first aspect, wherein the metal substrate is exposed.

[0009] Compared with a case where the metal substrate is covered with a protective layer or the like, when the metal substrate is exposed, deformation of the metal substrate due to pressure from an object is more likely to occur. Even in such a situation, deformation of the metal substrate can be suppressed by the metal substrate having a Vickers hardness of 230 HV or more. In other words, according to the second aspect, the effect of the metal substrate having a Vickers hardness of 230 HV or more becomes more pronounced.

[0010] A third aspect of the present invention is a superconducting conductor comprising an oxide superconducting wire according to the first or second aspect and at least one connecting wire for connecting a plurality of the oxide superconducting wires, wherein the connecting wire has a tape-shaped connecting metal substrate made of a nickel alloy, a connecting intermediate layer stacked on the connecting metal substrate, and a connecting oxide superconducting layer stacked on the connecting intermediate layer, and the connecting oxide superconducting layer is in contact with the oxide superconducting layers of a plurality of the oxide superconducting wires, and the corners of the connecting metal substrate are exposed.

[0011] In the third aspect, when the corners of the connecting metal substrate are exposed, the metal substrate may be deformed by being pressed against the corners. Even in such a situation, deformation of the metal substrate can be suppressed by setting the Vickers hardness of the metal substrate to 230 HV or more.

[0012] A fourth aspect of the present invention is a superconducting coil formed by winding a superconducting conductor according to the third aspect, wherein the corner portion of the connecting metal substrate abuts against the metal substrate of the oxide superconducting wire located radially outside the connecting metal substrate.

[0013] According to the fourth aspect, even when the corners of the connecting metal substrate are pressed against the metal substrate by tension applied when the superconducting coil is wound, deformation of the metal substrate can be suppressed.

[0014] According to the above aspects of the present invention, it is possible to provide an oxide superconducting wire, a superconducting conductor, and a superconducting coil in which the deterioration of superconducting properties due to a pressing force in the thickness direction is suppressed.

[0015] Fig. 1 is a cross-sectional view along the thickness direction and longitudinal direction of an oxide superconducting wire according to an embodiment of the present invention; Fig. 2 is a cross-sectional view along the thickness direction and longitudinal direction of a superconducting conductor according to an embodiment of the present invention; Fig. 3 is a perspective view of a superconducting coil according to an embodiment of the present invention; Fig. 4 is a cross-sectional view along the radial direction and axial direction of a superconducting coil according to an embodiment of the present invention; Fig. 5 is an explanatory diagram of a compression test.

[0016] The oxide superconducting wire, superconducting conductor, and superconducting coil of this embodiment will be described below with reference to the drawings. As shown in Fig. 1, the oxide superconducting wire 10 includes a metal substrate 11, an intermediate layer 12, an oxide superconducting layer 13, and a protective layer 14. Hereinafter, the metal substrate 11, the intermediate layer 12, the oxide superconducting layer 13, and the protective layer 14 may be collectively referred to as a "superconducting laminate."

[0017] Each of the metal substrate 11, the intermediate layer 12, the oxide superconducting layer 13, and the protective layer 14 is formed in a tape shape and is laminated in this order in the thickness direction of the metal substrate 11 (the thickness direction of the oxide superconducting wire 10).

[0018] As shown in Fig. 2, the superconducting conductor 1 of this embodiment includes a plurality of oxide superconducting wires 10 and at least one connecting wire 20. For ease of explanation, as shown in Fig. 2, one of the oxide superconducting wires 10 connected by the connecting wire 20 may be referred to as a first wire 10A, and the other oxide superconducting wire 10 may be referred to as a second wire 10B. The connecting wire 20 has the function of connecting two oxide superconducting wires 10 (the first wire 10A and the second wire 10B). The number of oxide superconducting wires 10 and connecting wires 20 included in the superconducting conductor 1 can be changed. The greater the number of oxide superconducting wires 10 and connecting wires 20, the longer the superconducting conductor 1 can be.

[0019] 3, the superconducting coil 100 of this embodiment is formed by winding a superconducting conductor 1. That is, the superconducting coil 100 includes a plurality of oxide superconducting wires 10 and at least one connecting wire 20. Such a superconducting coil 100 can be used in a superconducting magnet, a superconducting motor, or the like.

[0020] (Direction Definition) In FIG. 1 and other figures, the Z axis indicates the direction along the longitudinal direction of the oxide superconducting wire 10. The Y axis is perpendicular to the Z axis direction and indicates the direction along the thickness direction of the oxide superconducting wire 10. The Y axis direction is also the direction in which the layers 11 to 14 are stacked. In FIG. 3, the dashed-dotted line O indicates the central axis of the superconducting coil 100. The R axis indicates the radial direction of the superconducting coil 100. In other words, the R axis is perpendicular to the central axis O. In this specification, with respect to the oxide superconducting wire 10, the Y axis direction may be referred to as the thickness direction Y and the Z axis direction may be referred to as the longitudinal direction Z. Furthermore, with respect to the superconducting coil 100, the direction along the central axis O may be referred to as the axial direction and the R axis direction may be referred to as the radial direction R. The radial direction R of the superconducting coil 100 coincides with the thickness direction Y of the oxide superconducting wire 10.

[0021] 1, a specific example of the metal constituting the metal substrate 11 is a nickel alloy such as Hastelloy (registered trademark). The thickness of the metal substrate 11 may be adjusted appropriately depending on the purpose, and is within the range of 10 to 1000 μm, for example.

[0022] The intermediate layer 12 is laminated on the metal substrate 11 (on the upper surface of the metal substrate 11). The configuration of the intermediate layer 12 is not limited to the example shown in FIG. 1 . For example, the intermediate layer 12 may have a multilayer structure. In this case, the intermediate layer 12 may have, in order from the metal substrate 11 toward the oxide superconducting layer 13, a diffusion prevention layer, a bed layer, an orientation layer, a cap layer, and the like. These layers are not necessarily provided one by one; some layers may be omitted, or two or more layers of the same type may be repeatedly laminated. The intermediate layer 12 may be a metal oxide. By forming the oxide superconducting layer 13 on the upper surface of the intermediate layer 12 with excellent orientation, an oxide superconducting layer with excellent orientation can be easily obtained.

[0023] The oxide superconducting layer 13 is laminated on the intermediate layer 12 (on the upper surface of the intermediate layer 12). The oxide superconducting layer 13 is composed of an oxide superconductor. Examples of oxide superconductors constituting the oxide superconducting layer 13 include RE-Ba-Cu-O-based oxide superconductors (REBCO-based oxide superconductors) represented by the general formula REBaCuOy (RE123). The rare earth element RE may be one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In the general formula of RE123, y is 7-x (oxygen deficiency amount x: approximately 0 to 1). The ratio of RE:Ba:Cu is not limited to 1:2:3 and may be non-stoichiometric. The thickness of the oxide superconducting layer 13 is, for example, in the range of 0.5 to 5 μm. The oxide superconducting layer 13 can be formed by a PLD (pulsed laser ablation) film formation method or the like.

[0024] Artificial pins made of a different material may be introduced as artificial crystal defects into the oxide superconducting layer 13. Examples of the different material used to introduce the artificial pins into the oxide superconducting layer 13 include at least one material such as BaSnO3 (BSO), BaZrO3 (BZO), BaHfO3 (BHO), BaTiO3 (BTO), SnO2, TiO2, ZrO2, LaMnO3, and ZnO.

[0025] The protective layer 14 is laminated on the oxide superconducting layer 13 (on the upper surface of the oxide superconducting layer 13). The protective layer 14 has functions such as bypassing overcurrent that occurs in the event of an accident and suppressing chemical reactions that occur between the oxide superconducting layer 13 and layers provided on the protective layer 14. Examples of materials for the protective layer 14 include silver (Ag), copper (Cu), gold (Au), gold-silver alloys, other silver alloys, copper alloys, and gold alloys. Alternatively, the protective layer 14 may be a composite layer formed by laminating multiple layers of these metals. The thickness of the protective layer 14 is, for example, within the range of 1 to 100 μm. The protective layer 14 may be composed of two or more metals or two or more metal layers. The protective layer 14 can be formed by vapor deposition, sputtering, or the like.

[0026] 2 , the connecting wire 20 has a connecting metal substrate 21, a connecting intermediate layer 22, and a connecting oxide superconducting layer 23. The connecting metal substrate 21 can be made of the same material as the metal substrate 11. The connecting intermediate layer 22 can be made of the same material as the intermediate layer 12. The connecting oxide superconducting layer 23 can be made of the same material as the oxide superconducting layer 13. However, the materials of the connecting metal substrate 21, the connecting intermediate layer 22, and the connecting oxide superconducting layer 23 may be different from the materials of the metal substrate 11, the intermediate layer 12, and the oxide superconducting layer 13. The connecting wire 20 may be formed with a connecting protective layer (not shown) that covers the connecting oxide superconducting layer 23. When connecting to the oxide superconducting wire 10 described below, the connecting protective layer can be removed from the portion overlapping the oxide superconducting wire 10, and the exposed connecting oxide superconducting layer 23 can be overlapped with the oxide superconducting layer 13 of the oxide superconducting wire 10.

[0027] As shown in Fig. 2, the protective layer 14 is not formed on the portion of the oxide superconducting wire 10 that is connected by the connecting wire 20. For example, when manufacturing the oxide superconducting wire 10, the protective layer 14 may be formed on the entire oxide superconducting wire 10. In this case, when manufacturing the superconducting conductor 1, the protective layer 14 may be partially removed. Methods for partially removing the protective layer 14 include polishing and etching. Alternatively, when manufacturing the oxide superconducting wire 10, a portion without the protective layer 14 may be provided in advance.

[0028] In the portion of the oxide superconducting wire 10 where the protective layer 14 is not provided, the oxide superconducting layer 13 is exposed. The connecting oxide superconducting layer 23 of the connecting wire 20 is arranged so as to contact the exposed oxide superconducting layer 13. By arranging the connecting oxide superconducting layer 23 across multiple oxide superconducting layers 13, these oxide superconducting layers 13 can be connected to each other. In the portion where the connecting wire 20 is arranged, the metal substrate 11, intermediate layer 12, oxide superconducting layer 13, connecting oxide superconducting layer 23, connecting intermediate layer 22, and connecting metal substrate 21 are arranged in this order in the thickness direction Y. In FIG. 2 , corners 21 a of the connecting metal substrate 21 are located at the ends of the connecting wire 20 in the thickness direction Y and the longitudinal direction Z.

[0029] In the embodiment shown in Figure 2, the exposed connecting oxide superconducting layer 23 of the connecting wire 20 and the exposed oxide superconducting layer 13 of the oxide superconducting wire 10 are arranged to be in contact with each other, but the connecting protective layer (not shown) formed on the connecting wire 20 and the protective layer 14 formed on the oxide superconducting wire 10 may also be connected to each other via a low-melting point metal such as solder.

[0030] FIG. 4 is a cross-sectional view of a portion of the superconducting coil 100 shown in FIG. 3 where a connecting wire 20 is provided. The superconducting coil 100 is formed by winding a superconducting conductor 1 having a structure in which a plurality of oxide superconducting wires 10 are connected. Therefore, in the superconducting coil 100, a plurality of oxide superconducting wires 10 that were originally separate are adjacent to each other in the radial direction R. FIG. 4 shows a state in which a third wire 10C is located radially outside a first wire 10A and a second wire 10B. The first wire 10A, the second wire 10B, and the third wire 10C have similar layer structures. Note that, depending on the relationship between the radius of the superconducting coil 100 and the length of the oxide superconducting wire 10, the same oxide superconducting wires 10 may overlap in the radial direction R.

[0031] Here, tension is applied when the superconducting conductor 1 is wound. Due to this tension, the corner 21a of the connecting metal substrate 21 comes into contact with the metal substrate 11 of the third wire 10C, which is located on the outer side in the radial direction R. Then, the corner 21a is pressed against the metal substrate 11 of the third wire 10C. At this time, the pressing force acting on the corner 21a in the thickness direction Y has a magnitude corresponding to the tension. In other words, the greater the tension during winding, the greater the pressing force with which the corner 21a is pressed against the metal substrate 11.

[0032] The corners 21a are pressed against the metal substrate 11 in the radial direction R, which may cause deformation of the metal substrate 11. Furthermore, since the oxide superconducting layer 13 is less likely to deform than the metal substrate 11, it may be unable to follow the deformation of the metal substrate 11, resulting in deterioration of the oxide superconducting layer 13. Deterioration of the oxide superconducting layer 13 due to deformation of the metal substrate 11 reduces the characteristics of the superconducting coil 100. Specific examples of deterioration of the oxide superconducting layer 13 due to deformation of the metal substrate 11 include cracks and peeling.

[0033] Therefore, in this embodiment, the Vickers hardness of the metal substrate 11 is set to 230 HV or more. By specifying the hardness of the metal substrate 11 in this way, it is possible to suppress deterioration of the oxide superconducting layer 13 that accompanies deformation of the metal substrate 11. As a result, it is possible to ensure the characteristics of the superconducting coil 100.

[0034] The above embodiment will be described below using specific examples.

[0035] As shown in Table 1 below, oxide superconducting wires 10 with sample numbers 1 to 14 were prepared. The Vickers hardness of the metal substrate 11 differed from one another in each sample, but the materials and dimensions of the metal substrate 11, intermediate layer 12, and oxide superconducting layer 13 were similar. The metal substrate 11 of sample numbers 1 to 14 was made of a nickel alloy with the same composition, but the rolling reduction ratios were different. The different rolling reduction ratios resulted in different Vickers hardness values. Generally, the greater the rolling reduction ratio, the greater the Vickers hardness. For each sample, Vickers hardness was measured at five different measurement points in the width direction on a cross section perpendicular to the longitudinal direction Z. All five measurement points were located near the center of the metal substrate 11 in the width direction. The maximum and minimum Vickers hardness values ​​measured in this manner were extracted and listed in Table 1. For example, for sample number 1, the Vickers hardness at the five measurement points was within the range of 207 to 215 HV.

[0036]

[0037] In each sample, the thickness of the metal substrate 11 was 0.05 mm. The width of the metal substrate 11 was 4 mm. For each sample, the critical current Ic0 was measured before the compression test. Then, the compression test was performed using a test apparatus such as that shown in FIG. 5. Specifically, a test piece P made of a nickel alloy having the same material and rolling ratio as the metal substrate 11 of each sample was placed on a stage S. Each sample was placed on this test piece P. At this time, the corner p1 of the test piece P was in contact with the metal substrate 11.

[0038] In the state shown in Fig. 5, a pressing cover C was pressed from the protective layer 14 side of each sample with a pressing force of 400 N. After the compression test, the critical current Ic was measured for each sample, and the value of Ic / Ic0 was calculated. For example, for sample No. 1, the critical current Ic after the compression test was reduced to 0.93 times the critical current Ic0 before the compression test. The pressing force (400 N) in the compression test was determined taking into account that the tension when forming the superconducting coil 100 was approximately 200 N.

[0039] When the value of Ic / Ic0 is 0.99 or more, it means that the critical current value has not substantially changed due to the compression test, or if it has changed, it is within an acceptable range. Therefore, when the value of Ic / Ic0 is 0.99 or more, it is determined that the oxide superconducting layer 13 has not deteriorated and is judged as OK. When the value of Ic / Ic0 is below 0.99, it is determined that the oxide superconducting layer 13 has deteriorated and is judged as NG.

[0040] As shown in Table 1, for sample numbers 1 and 2, which had a Vickers hardness of 227 HV ​​or less, the Ic / Ic0 value was below 0.99 and they were judged to be NG. In sample numbers 1 and 2, the decrease in critical current due to the compression test is thought to be due to insufficient hardness of the metal substrate 11. In other words, it is thought that the corner p1 of the test piece P was pressed strongly against the metal substrate 11, causing deformation of the metal substrate 11 and resulting in a decrease in the superconducting properties.

[0041] In contrast, for sample numbers 3 to 14, which had a Vickers hardness of 230 HV or more, the Ic / Ic0 value was 0.99 or more and was judged to be OK. It is believed that the Vickers hardness of 230 HV or more prevented the metal substrate 11 from deforming even when the corner p1 of the test piece P was pressed strongly against the metal substrate 11.

[0042] From the above results, it was confirmed that the deterioration of the superconducting properties due to the pressing force in the thickness direction can be suppressed by setting the Vickers hardness of the metal substrate 11 to 230 HV or more. Although the Vickers hardness of the metal substrate 11 in Table 1 is 618 HV or less, it is believed that the same effect can be obtained even if the Vickers hardness is 618 HV or more.

[0043] Furthermore, in this embodiment, an oxide superconducting wire 10 is employed in which the metal substrate 11 is exposed. When the metal substrate 11 is exposed in this manner, the metal substrate 11 is more likely to deform when pressed by the corners 21 a of the connecting metal substrate 21, and therefore the effect of making the Vickers hardness of the metal substrate 11 230 HV or higher becomes significant. However, even when the metal substrate 11 is covered with, for example, a thin film or the like, deformation of the metal substrate 11 can occur when the corners 21 a of the connecting metal substrate 21 are pressed. Therefore, the effect of this embodiment can be expected even when the metal substrate 11 is not exposed.

[0044] The superconducting conductor 1 of this embodiment includes a plurality of oxide superconducting wires 10 and at least one connecting wire 20 connecting the plurality of oxide superconducting wires 10, the connecting wire 20 having a tape-shaped connecting metal substrate 21 made of a nickel alloy, a connecting intermediate layer 22 laminated on the connecting metal substrate 21, and a connecting oxide superconducting layer 23 laminated on the connecting intermediate layer 22, the connecting oxide superconducting layer 23 being in contact with the oxide superconducting layers 13 of the plurality of oxide superconducting wires 10, and corners 21 a of the connecting metal substrate 21 being exposed. The superconducting coil 100 is formed by winding the superconducting conductor 1, and the corners 21 a of the connecting metal substrate 21 are in contact with the metal substrate 11 of the oxide superconducting wire 10 located radially outward of the connecting metal substrate 21. In such a superconducting conductor 1 and superconducting coil 100, deformation of the metal substrate 11 caused by the corners 21a being pressed against the metal substrate 11 can be suppressed.

[0045] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0046] For example, in the above embodiment, the superconducting conductor 1 is used as the superconducting coil 100. However, the superconducting conductor 1 does not necessarily have to be used as the superconducting coil 100. Alternatively, the oxide superconducting wire 10 may be used alone without constituting the superconducting conductor 1. Even when the oxide superconducting wire 10 is in a standalone state, a pressing force may act on the oxide superconducting wire 10 in the thickness direction Y. As a specific example, in a production line for the oxide superconducting wire 10, rollers for transporting the oxide superconducting wire 10 may come into contact with the metal substrate 11, causing a pressing force to act. Even in such a case, by making the Vickers hardness of the metal substrate 11 230 HV or higher, the effect of suppressing deterioration in the superconducting properties can be obtained.

[0047] Furthermore, not only the corners 21 a of the connecting metal substrate 21 but also other structures may be pressed against the metal substrate 11. For example, a conveying roller or the like in a production line for the oxide superconducting wire 10 may be pressed against the metal substrate 11. Therefore, the presence of the corners 21 a of the connecting metal substrate 21 is not an essential requirement.

[0048] In addition, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate, without departing from the spirit of the present invention.

[0049] REFERENCE SIGNS LIST 1... superconducting conductor 10... oxide superconducting wire 11... metal substrate 12... intermediate layer 13... oxide superconducting layer 20... connecting wire 21... connecting metal substrate 21a... corner portion 22... connecting intermediate layer 23... connecting oxide superconducting layer 100... superconducting coil

Claims

1. An oxide superconducting wire comprising: a tape-shaped metal substrate made of a nickel alloy; an intermediate layer laminated on the metal substrate; and an oxide superconducting layer laminated on the intermediate layer, wherein the Vickers hardness of the metal substrate is 230 HV or more.

2. The oxide superconducting wire according to claim 1, wherein the metal substrate is exposed.

3. A superconducting conductor comprising a plurality of the oxide superconducting wires according to claim 1 or 2, and at least one connecting wire connecting the plurality of the oxide superconducting wires, wherein the connecting wire has a tape-shaped connecting metal substrate made of a nickel alloy, a connecting intermediate layer laminated on the connecting metal substrate, and a connecting oxide superconducting layer laminated on the connecting intermediate layer, the connecting oxide superconducting layer being in contact with the oxide superconducting layers of the plurality of the oxide superconducting wires, and the corners of the connecting metal substrate being exposed.

4. A superconducting coil formed by winding the superconducting conductor according to claim 3, wherein the corners of the connecting metal substrate are in contact with the metal substrate of the oxide superconducting wire located radially outside the connecting metal substrate.

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